The following is from this forum sometime ago--I saved it in my MB E420 Notes file. Thus, I'm not the author, but fwiw, it appears responsive to your inquiry:
"To start with the E420 doesn't have an over-voltage relay like the E320/C280 cars! Stalling can be caused by carbon build-up on the throttle plate. The throttle body bolts directly to the intake manifold. There is a small hole drilled into the butterfly(M119) and if carbon builds up on this hole the car will die at times
Check your throttle actuator. You can try moving around the actuator cable as it idles. Sometimes they have internal potentiometer problems. Might be better to have a tech check it. This is a common problem on these cars.
Many times CLEANING the throttle body area with a scotch-brite pad will eliminate the stalling problem.
99% of the time, it is the throttle body. I have replaced several and fixed all of the complaints."